1. Field of the Invention
The present invention relates to an image forming apparatus and a method of driving and controlling a head.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, a plotter, or a combined machine thereof, an ink jet recording device is known, which is a liquid ejecting and recording-type image forming apparatus using a liquid ejection head that ejects a liquid droplet as a recording head.
In the liquid ejection head, a water repellant film is formed on a nozzle surface on which a nozzle for ejecting liquid droplets is formed in order to obtain stable droplet ejection characteristic. However, when unevenness or deviation is caused in distribution of wettability in the vicinity of the nozzle, or an ink is solidified in the vicinity of the nozzle, due to abrasion or exfoliation of the water repellant film, a meniscus formed in the nozzle at meniscus oscillation becomes uneven, and the ink droplet ejected through the nozzle is more likely to bend.
Especially, immediately after a large droplet or a middle droplet having large droplet sizes is ejected, the meniscus overflows in the vicinity of the nozzle, and the first liquid droplet ejected next tends to bend. When the droplet bending is generated, the image quality is decreased.
Therefore, conventionally, a configuration is known, in which a ejection pulse including a drive pulse that contributes to formation of a droplet shape having a plurality of droplet sizes is generated, a plurality of drive pulses that contributes to the formation of a droplet shape of a drive waveform includes a drive pulse including a waveform element that allows a pressure liquid chamber to expand in at least two stages, and pulls in the meniscus just before allowing the pressure liquid chamber to contact and ejecting liquid droplets, and the drive pulse has a time interval Ts between a first-stage expansion start point of the pressure liquid chamber and a second-stage expansion start point of the pressure liquid chamber that satisfies a relationship of 0.3Tc≦Ts≦0.7Tc (Japanese Laid-open Patent Publication No. 2011-062821).
As described above, there is an advantage that the droplet bending is less likely to be caused when the pressure liquid chamber (individual liquid chamber) is expanded and the meniscus is pulled in two stages just before the pressurized chamber is contracted and the liquid droplets are ejected, compared with a case in which the pressure liquid chamber is expanded and the meniscus is pulled in a single stage.
However, in the configuration disclosed in Japanese Laid-open Patent Publication No. 2011-062821, a first ejection pulse that ejects liquid droplets including liquid droplets having respective droplet sizes includes a pulling-in waveform element that allows the pressure liquid chamber (individual liquid chamber) to expand in two stages.
Therefore, the waveform length of the entire drive waveform becomes longer as the droplet sizes to be ejected are increased, and the drive frequency is reduced and the print speed is decreased.
Therefore, there is a need to reduce ejection bending without reducing a drive frequency.